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Genetic counseling: Cystic Fibrosis - Prenatal Diagnosis-1
Cystic Fibrosis - Prenatal Diagnosis Introduction and Contracting *What are your main reasons for seeking genetic counseling? *Do you have any particular questions or concerns you would like to discuss? *Address any immediate concerns or indicate that they will be addressed later during the discussion *Outline the session including the information they want to know *First I'll obtain more information about medical and family history to determine if there is anything else that we may want to discuss today *Then we can discuss cystic fibrosis and answer any questions you have Obtain Medical and Family History Review Genes and Chromosomes *Sometimes it is helpful to review some basic genetics principles because it is not something most people think about every day. *Review genes and chromosomes and explain autosomal recessive inheritance FACTS ABOUT CF CF Overview *CF is one of the most common inherited diseases (affects 1 in 3300 live births in US) *occurs in individuals of all races and ethnicities, but is most common in Caucasians *Due to changes in both copies of a gene that instructs the body about how to make a protein channel that transports sodium and chloride into cells that line certain organs *These channels are either not made or don't work properly *This leads to production of thick mucus in the lungs which then leads to an increased risk of infections and pneumonia that may require periods of hospitalization *It can also cause interference with digestion, which can lead to diarrhea and poor growth *It also often causes infertility in males and may cause decreased fertility in females Features of CF *normal intelligence *features may include *chronic sino-pulmonary disease: cough, sputum production, wheezing, obstructive lung disease, chronic chest radiograph abnormalities, digital clubbing *gastrointestinal/ nutritional abnormalities: malabsorption/ pancreatic insufficiency (foul, bulky, fatty stools) distal intestinal obstructive syndrome, rectal prolapse, recurrent pancreatitis, chronic hepatobiliary disease, failure to thrive, hypoproteinemia, fat soluble vitamin deficiencies *infertility: 98% of males with CF infertile due to unilateral or bilateral agenesis of vas deferens decreased fertility in females due to abnormal cervical mucus that can contribute to infertility Diagnosis *median age diagnosed is 6-8 months (2/3 dx before age 1) *diagnoses established in people with one or more phenotypic features and one of following *presence of 2 disease-causing mutations in the CFTR (cystic fibrosis transmembrane regulator) gene *two abnormal quantitative sweat chloride values (the "gold standard") *painless, relatively inexpensive, definitive answer) *abnormal value for the transepithelial nasal potential difference (NPD) *diagnosis established in absence of phenotypic characteristics when *confirmed dx of sibling and abnormal sweat chloride value or presence of same two mutations as in the sibling Prognosis *survival increased from 18 years 1976 to 30.1 years 1995 currently approximated at 33 yrs (geneclinics) *pulmonary disease major cause morbidity and mortality *patients with pancreatic sufficiency (<10%) have milder course and greater survival (56 yrs 1995 CFF Patient Registry *wide variability in disease expression Incidence *Caucasians 1/2,500 *African-Americans 1/18,000 *Asian Americans 1/90,000 *30,000 affected in US 8,000,000 carriers in US *carrier rates see chart in visual aids CF gene and common mutations *located on 7q *250,000 bp, 27 exons and 1,480 aa's *functions as a regulated chloride channel in epithelial cells *over 900 known mutations (most point mut. or small del.) *genotype/phenotype correlation (both severe and mild mutations) *delta F508 most common (30-80% of mutations) CF Carrier Screening *As mentioned CF occurs more frequently in Caucasians than other ethnicities (one in 25,000 Caucasians affected and 1 in 28 are carriers) *AR inheritance, both parents must be carriers to have child with CF *a blood test is offered that can determine if an individual is a carrier of CF *assess whether interested in this testing *testing at CHMC now offered and screens for 25 of most common mutations *now CHMC does the panel for ________???? *GENZYME panel of 87 *carrier detection rate with the panel is 90% if of Northern European Descent and 70% if of Southern European descent. *The 87 mutation analysis by genzyme detects 85-90% of carriers if Caucasian *cost was $265 when done through CHMC, but sent to genzyme CHMC added on a lab fee Results take about 2 weeks according to genzyme Options for Pregnancy and Future Pregnancies if Both Were Carriers *Testing can determine if a fetus is affected before they are born *Amnio can be performed to test and see if fetus has CF and it is greater than 99% accurate if the mutations that parents carry are known *Future pregnancies also have option of CVS performed earlier than amnio 10-12 weeks *Describe if interested *preimplantation genetic diagnosis-Where they perform genetic testing on embryos obtained using in vitro fertilization techniques. Then only implant those that don't have CVS *If interested would be important to review costs and success rates Review *Assess if there are any questions or other concerns throughout the session *Assess how they feel about carrier testing *Offer patient literature on CF Psychosocial Considerations *May be nervous about pregnancy due to earlier loss *Normalize early losses *May not know much about partner's history *Check to determine who she has for support family friends *Assess their experience with CF and make certain to explain that the symptoms and how affected someone is varies even among family members with same mutation *May think risk is higher than it is for CF so get a feel for how likely she thinks it is References *www.geneclinics.org *Bianchi, D.W., Crombleholme T.M., D'alton, M.E. Fetology: Diagnosis & Management of the Fetal Patient. McGraw Hill, New York, 2000 *Kuller, J.A., Chescher, N.C., Cefalo, R.C. Prenatal Diagnosis and Reproductive Genetics. Mosby Year Book Inc. 1996. *http://www.reproductivegenetics.com/preimplantation.shtml *www.geneclinics.com Notes The information in this outline was last updated in 2002. This material has been imported fom the wikibook "Genetic counseling"[ http://en.wikibooks.org/wiki/Genetic_counseling] under the GNU Free Documentation License.